UPSC Prelims 2012 · GS Paper I
Question 99: Environment and Ecology
What would happen if phytoplankton of an ocean is completely destroyed for some reason?
- 1.The ocean as a carbon sink would be adversely affected.
- 2.The food chains in the ocean would be adversely affected.
- 3.The density of ocean water would drastically decrease.
Select the correct answer using the codes given below :
AnswerUPSC’s answer is (a).
Phytoplankton photosynthesise, taking carbon dioxide from the water and carrying carbon to the deep sea, so losing them would weaken the ocean as a carbon sink. They are also the base of marine food chains, so everything above them would suffer. They have no major effect on the density of seawater, which depends mainly on temperature and salinity.
- 1. Phytoplankton take up carbon dioxide, so the ocean sink would weaken.
- 2. They are the base of marine food chains.
- 3. Density depends on temperature and salinity, not on phytoplankton.
How you could have got this
- If you were sure statement 1 is correct, (b) and (c) go: each of them leaves 1 out.
What you needed to know: Phytoplankton take up carbon dioxide, so the ocean sink would weaken.
- Then, if you were sure statement 3 is not correct, (d) goes: it includes 3.
What you needed to know: Density depends on temperature and salinity, not on phytoplankton.
Only (a) is left. You didn’t need statement 2.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Correct: the carbon sink and food chains would suffer.
- (b) Incomplete: the carbon sink would also be affected.
- (c) Wrong: seawater density depends on temperature and salinity, not phytoplankton.
- (d) Wrong: statement 3 on drastic density change is false.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper I, Series A. The paper on upsc.gov.in.